Non-collinear spectral coherent combining (NCSCC) of ultrashort pulses is analyzed. 2D modeling of the electromagnetic field is performed in case of NCSCC using two or three pulses with different wavelengths. In the case of two pulses, a potentially unwanted spatio-temporal structure of the field appears, corresponding to spatial and temporal modulation of the pulse. By using NCSCC of three 62 fs long pulses with different spectral composition, such spatial-temporal coupling is eliminated and the combined pulse duration in the focal region drops to less than half. The method is scalable to a large number of ultrashort pulses.

The development of graphene-based materials for optical limiting functionality is an active field of research. Optical limiting for femtosecond laser pulses in the infrared-B (IR-B) (1.4–3 μm) spectral domain has been investigated to a lesser extent than that for nanosecond, picosecond and femtosecond laser pulses at wavelengths up to 1.1 μm. Novel nonlinear optical materials, glassy graphene oxide (GO)-based silico-phosphate composites, were prepared, for the first time to our knowledge, by a convenient and low cost sol-gel method, as described in the paper, using tetraethyl orthosilicate (TEOS), H₃PO₄ and GO/reduced GO (rGO) as precursors. The characterisation of the GO/rGO silico-phosphate composite films was performed by spectroscopy (Fourier-transform infrared (FTIR), Ultraviolet–Visible-Near Infrared (UV-VIS-NIR) and Raman) and microscopy (atomic force microscopy (AFM) and scanning electron microscopy (SEM)) techniques. H₃PO₄ was found to reduce the rGO dispersed in the precursor’s solution with the formation of vertically agglomerated rGO sheets, uniformly distributed on the substrate surface. The capability of these novel graphene oxide-based materials for the optical limiting of femtosecond laser pulses at 1550 nm wavelength was demonstrated by intensity-scan experiments. The GO or rGO presence in the film, their concentrations, the composite films glassy matrix, and the film substrate influence the optical limiting performance of these novel materials and are discussed accordingly.

It is shown that in the focus of ultra-short pulses of duration t, the equivalent relation s = ct, where c is the speed of light and s the spatial extent of the pulse of the collimated pulse, does not hold. While the duration of one pulse is constant and independent of the measurement point, the spatial extension of the ultra-short pulse can be spatially shorter a factor more than 10 compared to the one obtained from the usual relation. The result is explained in correspondence with the extension of the Rayleigh range. Few femtosecond long gamma bursts can thus be generated in Thomson backscattering experiments performed in the lambda cube regime.

A versatile method to enhance the laser pulse intensity by one order of magnitude from 8 x 10(20) W/cm(2) using a single plastic micro-cone target is proposed in this Letter. We found an increase of the initial laser pulse intensity by more than 10 times for a micro-cone tip diameter of 5 mu m upon performing two-dimensional particle-in-cell simulations. Numerical simulations of the spatio-temporal electromagnetic field distribution are used to replicate similar dependence of the maximum laser intensity to the cone tip diameter. (C) 2020 Optical Society of America

We study the interaction of an ultra-high intensity laser pulse with plastic nano-layered flat-top cone targets by performing particle-in-cell simulations. Also, we analyze the spatio-temporal dynamics of the electromagnetic field based on the finite-difference time-domain method in order to isolate the geometric effects which affect the incoming laser-plasma interaction. We consider an ultra-high intensity laser pulse with linear and circular polarization. We have determined the optimum diameter of the nanospheres for a given nano-layer foil thickness for which it can be obtained beams of very energetic protons with low angular divergence. We point out that the protons are accelerated by a hybrid mechanism composed of target normal sheath acceleration and radiation pressure acceleration. This numerical study will allow to prepare and optimize first laser ion acceleration experiments on Extreme Light Infrastructure-Nuclear Physics and other PW laser facilities.

The present work reports the development of an optimized ultra-intense laser—solid target interaction system which aims to achieve higher intensities for different pulse durations, down to few-cycle regime, considering different micro-structured profiles of the internal cone target walls. A spatio-temporal analysis of the electromagnetic field in the interaction area is elaborated in order to provide a complex description of this approach. The numerical analysis is made by using the finite difference time domain (FDTD) method. The results are explained in correspondence with the extension of the Rayleigh range and it is relevant for a wide range of ultra-short and ultra-intense laser experiments planned at laser facilities in petawatt regimes.